The present invention relates to a method of depositing a coating film on a substrate by sputtering in a vacuum apparatus which can control a reduced pressure atmosphere.
A technique has conventionally been attempted which comprises closely arranging two cathodes, disposing targets made of different materials respectively on the cathodes, and depositing a coating film comprising the materials of the targets on a substrate by sputtering. In this case, a power supply for applying a negative voltage to each cathode is used. Namely, this technique employs separate electrical circuits for the respective cathodes.
In the sputtering method described above, the glow discharges generated for sputtering target materials are not stable, i.e., an abnormal discharge generates frequently. The conventional technique hence has had a problem that a coating film having a desired thickness cannot be obtained or the coating film deposited has pinholes or adherent foreign substances.
In the technique in which targets made of different materials are disposed respectively on two cathodes arranged so as to be adjacent to each other and a coating film comprising the two target materials is to be deposited on a substrate surface, it is necessary that the cathodes should be closely arranged. In this case, the glow discharge plasmas generating on the respective target surfaces are close to each other due to the magnetic field in the magnetron. As a result, target components ejected from one target accumulate on the neighboring target surface to cover the region where the target is to be bombarded with positive ions (erosion region) with an electrical insulating film. This covering causes the glow discharge plasma to be unstable and unable to last. Namely, there has been a problem that stable and continuous film deposition becomes impossible. This problem is serious especially when an oxide coating film or a semiconductor coating film is to be deposited on a substrate, and brings about fatal results. Specifically, abnormal discharges frequently occur and glow discharges stop occasionally, making it impossible to continue coating film deposition.
The problem may be overcome by arranging two cathodes at a larger distance from each other. However, the increased distance between cathodes poses an essential problem that the target materials respectively ejected from the two targets cannot be simultaneously sputtered as a coating film.
An object of the present invention is to provide a method in which targets differing in component or composition are disposed on two closely arranged cathodes, and atoms, molecules, or particles of the materials of the targets are simultaneously accumulated on a substrate surface by sputtering with stable glow discharges to thereby deposit a coating film comprising those two materials or compositions.
The present invention has been achieved in order to eliminate the problem described above, and provides a method of film deposition on a substrate surface which comprises closely arranging a pair of cathodes in a vacuum apparatus in which an atmosphere having a reduced pressure can be prepared, applying a voltage thereto while alternately inverting the polarities thereof so that when one of the cathodes is used as a negative or positive electrode, then the other cathode is used as a positive or negative electrode, respectively, to generate glow discharges on targets respectively disposed on the two cathodes, and simultaneously bombarding the targets with positive ions resulting from the glow discharges to thereby sputter a coating film comprising the materials of the targets on a surface of a substrate, wherein the material of the target disposed on one of the cathodes differs from that of the target disposed on the other cathode and the film deposited on the substrate surface comprises both of the target materials.
In one embodiment of the method of the present invention, the cathodes as a pair are planar cathodes arranged so that the longer sides of one of the cathodes are parallel to those of the other, and the substrate is passed in front of the cathodes in such a manner as to cross the cathodes in a direction perpendicular to the direction of the longer sides of the cathodes, whereby the coating film deposited has a concentration gradient in the thickness direction with respect to the concentration of each of the different target materials.
In another embodiment of the method of the present invention, the two cathodes are arranged so that one is surrounded by the other, whereby the different target materials in the coating film deposited are present as a mixture of both.
In still another embodiment of the method of the present invention, the target materials each is a metal.
In a further embodiment of the method of the present invention, the target materials each is an electroconductive metal oxide.